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This is the first item in the file.
struct Header { // Signature information unsigned long Signature; short MajorVersion; short MinorVersion; bool Dirty; // Size of structure values unsigned short HeaderSz; unsigned short PackageSz; unsigned short PackageFileSz; unsigned short VersionSz; unsigned short DependencySz; unsigned short ProvidesSz; unsigned short VerFileSz; // Structure counts unsigned long PackageCount; unsigned long VersionCount; unsigned long DependsCount; unsigned long PackageFileCount; // Offsets unsigned long FileList; // PackageFile unsigned long StringList; // StringItem unsigned long VerSysName; // StringTable unsigned long Architecture; // StringTable unsigned long MaxVerFileSize; // Allocation pools struct { unsigned long ItemSize; unsigned long Start; unsigned long Count; } Pools[7]; // Package name lookup unsigned long HashTable[2*1024]; // Package };
This must contain the hex value 0x98FE76DC which is designed to verify that the system loading the image has the same byte order and byte size as the system saving the image
These contain the version of the cache file, currently 0.2.
Dirty is true if the cache file was opened for reading, the client expects to have written things to it and have not fully synced it. The file should be erased and rebuilt if it is true.
*Sz contains the sizeof() that particular structure. It is used as an extra consistency check on the structure of the file. If any of the size values do not exactly match what the client expects then the client should refuse the load the file.
These indicate the number of each structure contained in the cache. PackageCount is especially useful for generating user state structures. See Package::Id for more info.
String representing the version system used for this cache
Architecture the cache was built against.
The maximum size of a raw entry from the original Package file (i.e. VerFile::Size) is stored here.
This contains the index of the first PackageFile structure. The PackageFile structures are singly linked lists that represent all package files that have been merged into the cache.
This contains a list of all the unique strings (string item type strings) in the cache. The parser reads this list into memory so it can match strings against it.
The Pool structures manage the allocation pools that the generator uses. Start indicates the first byte of the pool, Count is the number of objects remaining in the pool and ItemSize is the structure size (alignment factor) of the pool. An ItemSize of 0 indicates the pool is empty. There should be the same number of pools as there are structure types. The generator stores this information so future additions can make use of any unused pool blocks.
HashTable is a hash table that provides indexing for all of the packages. Each package name is inserted into the hash table using the following has function:
unsigned long Hash(string Str) { unsigned long Hash = 0; for (const char *I = Str.begin(); I != Str.end(); I++) Hash += *I * ((Str.end() - I + 1)); return Hash % _count(Head.HashTable); }
By iterating over each entry in the hash table it is possible to iterate over the entire list of packages. Hash Collisions are handled with a singly linked list of packages based at the hash item. The linked list contains only packages that match the hashing function.
This contains information for a single unique package. There can be any number of versions of a given package. Package exists in a singly linked list of package records starting at the hash index of the name in the Header->HashTable.
struct Pacakge { // Pointers unsigned long Name; // Stringtable unsigned long VersionList; // Version unsigned long CurrentVer; // Version unsigned long Section; // StringTable (StringItem) // Linked lists unsigned long NextPackage; // Package unsigned long RevDepends; // Dependency unsigned long ProvidesList; // Provides // Install/Remove/Purge etc unsigned char SelectedState; // What unsigned char InstState; // Flags unsigned char CurrentState; // State // Unique ID for this pkg unsigned short ID; unsigned long Flags; };
Name of the package.
Base of a singly linked list of version structures. Each structure represents a unique version of the package. The version structures contain links into PackageFile and the original text file as well as detailed information about the size and dependencies of the specific package. In this way multiple versions of a package can be cleanly handled by the system. Furthermore, this linked list is guaranteed to be sorted from Highest version to lowest version with no duplicate entries.
CurrentVer is an index to the installed version, either can be 0.
This indicates the deduced section. It should be "Unknown" or the section of the last parsed item.
Next link in this hash item. This linked list is based at Header.HashTable and contains only packages with the same hash value.
Reverse Depends is a linked list of all dependencies linked to this package.
This is a linked list of all provides for this package name.
These correspond to the 3 items in the Status field found in the status file. See the section on defines for the possible values.
SelectedState is the state that the user wishes the package to be in.
InstState is the installation state of the package. This normally should be OK, but if the installation had an accident it may be otherwise.
CurrentState indicates if the package is installed, partially installed or not installed.
ID is a value from 0 to Header->PackageCount. It is a unique value assigned by the generator. This allows clients to create an array of size PackageCount and use it to store state information for the package map. For instance the status file emitter uses this to track which packages have been emitted already.
Flags are some useful indicators of the package's state.
This contains information for a single package file. Package files are referenced by Version structures. This is a singly linked list based from Header.FileList
struct PackageFile { // Names unsigned long FileName; // Stringtable unsigned long Archive; // Stringtable unsigned long Component; // Stringtable unsigned long Version; // Stringtable unsigned long Origin; // Stringtable unsigned long Label; // Stringtable unsigned long Architecture; // Stringtable unsigned long Site; // Stringtable unsigned long IndexType; // Stringtable unsigned long Size; // Linked list unsigned long NextFile; // PackageFile unsigned short ID; unsigned long Flags; time_t mtime; // Modification time };
Refers the the physical disk file that this PacakgeFile represents.
This is the release information. Please see the files document for a description of what the release information means.
The site the index file was fetched from.
A string indicating what sort of index file this is.
Size is provided as a simple check to ensure that the package file has not been altered.
See Package::ID.
Provides some flags for the PackageFile, see the section on defines.
Modification time for the file at time of cache generation.
This contains the information for a single version of a package. This is a single linked list based from Package.Versionlist.
The version list is always sorted from highest version to lowest version by the generator. Also there may not be any duplicate entries in the list (same VerStr).
struct Version { unsigned long VerStr; // Stringtable unsigned long Section; // StringTable (StringItem) unsigned long Arch; // StringTable // Lists unsigned long FileList; // VerFile unsigned long NextVer; // Version unsigned long DependsList; // Dependency unsigned long ParentPkg; // Package unsigned long ProvidesList; // Provides unsigned long Size; unsigned long InstalledSize; unsigned long Hash; unsigned short ID; unsigned char Priority; };
This is the complete version string.
References the all the PackageFile's that this version came out of. FileList can be used to determine what distribution(s) the Version applies to. If FileList is 0 then this is a blank version. The structure should also have a 0 in all other fields excluding VerStr and Possibly NextVer.
This string indicates which section it is part of. The string should be contained in the StringItem list.
Architecture the package was compiled for.
Next step in the linked list.
This is the base of the dependency list.
This links the version to the owning package, allowing reverse dependencies to determine the package.
Head of the linked list of Provides::NextPkgProv, forward provides.
The archive size for this version. For Debian this is the size of the .deb file. Installed size is the uncompressed size for this version
This is a characteristic value representing this package. No two packages in existence should have the same VerStr and Hash with different contents.
See Package::ID.
This is the parsed priority value of the package.
Dependency contains the information for a single dependency record. The records are split up like this to ease processing by the client. The base of list linked list is Version.DependsList. All forms of dependencies are recorded here including Conflicts, Suggests and Recommends.
Multiple depends on the same package must be grouped together in the Dependency lists. Clients should assume this is always true.
struct Dependency { unsigned long Version; // Stringtable unsigned long Package; // Package unsigned long NextDepends; // Dependency unsigned long NextRevDepends; // Reverse dependency linking unsigned long ParentVer; // Upwards parent version link // Specific types of depends unsigned char Type; unsigned char CompareOp; unsigned short ID; };
The string form of the version that the dependency is applied against.
The index of the package file this depends applies to. If the package file does not already exist when the dependency is inserted a blank one (no version records) should be created.
Linked list based off a Version structure of all the dependencies in that version.
Reverse dependency linking, based off a Package structure. This linked list is a list of all packages that have a depends line for a given package.
Parent version linking, allows the reverse dependency list to link back to the version and package that the dependency are for.
Describes weather it is depends, predepends, recommends, suggests, etc.
Describes the comparison operator specified on the depends line. If the high bit is set then it is a logical or with the previous record.
See Package::ID.
Provides handles virtual packages. When a Provides: line is encountered a new provides record is added associating the package with a virtual package name. The provides structures are linked off the package structures. This simplifies the analysis of dependencies and other aspects A provides refers to a specific version of a specific package, not all versions need to provide that provides.
There is a linked list of provided package names started from each version that provides packages. This is the forwards provides mechanism.
struct Provides { unsigned long ParentPkg; // Package unsigned long Version; // Version unsigned long ProvideVersion; // Stringtable unsigned long NextProvides; // Provides unsigned long NextPkgProv; // Provides };
The index of the package that head of this linked list is in. ParentPkg->Name is the name of the provides.
The index of the version this provide line applies to.
Each provides can specify a version in the provides line. This version allows dependencies to depend on specific versions of a Provides, as well as allowing Provides to override existing packages. This is experimental.
Next link in the singly linked list of provides (based off package)
Next link in the singly linked list of provides for 'Version'.
VerFile associates a version with a PackageFile, this allows a full description of all Versions in all files (and hence all sources) under consideration.
struct pkgCache::VerFile { unsigned long File; // PackageFile unsigned long NextFile; // PkgVerFile unsigned long Offset; unsigned short Size; }
The index of the package file that this version was found in.
The next step in the linked list.
These describe the exact position in the package file for the section from this version.
StringItem is used for generating single instances of strings. Some things like Section Name are are useful to have as unique tags. It is part of a linked list based at Header::StringList.
struct StringItem { unsigned long String; // Stringtable unsigned long NextItem; // StringItem };
The string this refers to.
Next link in the chain.
All strings are simply inlined any place in the file that is natural for the writer. The client should make no assumptions about the positioning of strings. All stringtable values point to a byte offset from the start of the file that a null terminated string will begin.
Several structures use variables to indicate things. Here is a list of all of them.
#define pkgDEP_Depends 1 #define pkgDEP_PreDepends 2 #define pkgDEP_Suggests 3 #define pkgDEP_Recommends 4 #define pkgDEP_Conflicts 5 #define pkgDEP_Replaces 6
#define pkgOP_OR 0x10 #define pkgOP_LESSEQ 0x1 #define pkgOP_GREATEREQ 0x2 #define pkgOP_LESS 0x3 #define pkgOP_GREATER 0x4 #define pkgOP_EQUALS 0x5
The lower 4 bits are used to indicate what operator is being specified and the upper 4 bits are flags. pkgOP_OR indicates that the next package is or'd with the current package.
#define pkgSTATE_Unkown 0 #define pkgSTATE_Install 1 #define pkgSTATE_Hold 2 #define pkgSTATE_DeInstall 3 #define pkgSTATE_Purge 4
#define pkgSTATE_Ok 0 #define pkgSTATE_ReInstReq 1 #define pkgSTATE_Hold 2 #define pkgSTATE_HoldReInstReq 3
#define pkgSTATE_NotInstalled 0 #define pkgSTATE_UnPacked 1 #define pkgSTATE_HalfConfigured 2 #define pkgSTATE_UnInstalled 3 #define pkgSTATE_HalfInstalled 4 #define pkgSTATE_ConfigFiles 5 #define pkgSTATE_Installed 6
#define pkgFLAG_Auto (1 << 0) #define pkgFLAG_New (1 << 1) #define pkgFLAG_Obsolete (1 << 2) #define pkgFLAG_Essential (1 << 3) #define pkgFLAG_ImmediateConf (1 << 4)
Zero is used for unparsable or absent Priority fields.
#define pkgPRIO_Important 1 #define pkgPRIO_Required 2 #define pkgPRIO_Standard 3 #define pkgPRIO_Optional 4 #define pkgPRIO_Extra 5
#define pkgFLAG_NotSource (1 << 0) #define pkgFLAG_NotAutomatic (1 << 1)
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APT Cache File Format
$Id: cache.sgml,v 1.11 2003/02/12 15:05:44 doogie Exp $jgg@debian.org